This invention relates to a hydrogen-absorbing alloy, a secondary battery comprising a negative electrode containing the hydrogen-absorbing alloy, a hybrid car equipped with a secondary battery comprising a negative electrode containing the hydrogen-absorbing alloy, and an electromobile equipped with the aforementioned secondary battery.
Hydrogen-absorbing alloy has been noticed as being capable of safely and easily storing hydrogen as an energy source, and also as being useful as an energy exchange material or an energy storage material. Therefore, there have being proposed various applications of hydrogen-absorbing alloy as a new functional material. For example, hydrogen-absorbing alloy has been proposed to employ for the storage and transport of hydrogen, the storage and transport of heat, the conversion of heat energy to mechanical energy, the separation and purification of hydrogen, the separation of hydrogen isotope, a battery employing hydrogen as an active material, a catalyst in synthetic chemistry, and a temperature sensor.
Particularly, the application of a secondary battery which is capable of reversibly absorbing and desorbing hydrogen to the negative electrode of a secondary battery is extensively studied. In fact, some of secondary batteries of this kind are put to practical use. By the way, a secondary battery has been employed as a power source for various kinds of portable electronic apparatus of small size and light weight. These portable electronic apparatuses are now being increasingly enhanced in the performance, function and miniaturization thereof, so that in order to enable these portable electronic apparatuses to be operable for a long period of time, the discharge capacity per unit volume of the secondary battery is required to be increased. Additionally, it is also desired in recent years to make the secondary battery more light in weight, i.e. to increase the discharge capacity per unit weight of the secondary battery in addition to increasing the discharge capacity per unit volume thereof.
A rare earth element-based hydrogen-absorbing alloy of AB5 type is capable of reacting with hydrogen at the normal temperature and pressure, and is relatively excellent in chemical stability, so that this rare earth element-based hydrogen-absorbing alloy of AB5 type is now extensively studied as a prospective hydrogen-absorbing alloy for the secondary battery, and is actually put to practical use for a negative electrode of the secondary battery available on the market. However, the discharge capacity of this secondary battery placed on the market and provided with the negative electrode containing this AB5 type rare earth element-based hydrogen-absorbing alloy now reaches to as high as 80% or more of the theoretical capacity, so that any further increase in discharge capacity would be difficult.
By the way, there are a large number of the rare earth element-Ni based intermetallic compounds other than the aforementioned AB5 type rare earth element-based intermetallic compound. For example, Mat. Res. Bull., 11, (1976) 1241 describes that an intermetallic compound containing a larger quantity of rare earth element as compared with the AB5 type compound is capable of absorbing a larger quantity of hydrogen in the vicinity of room temperature as compared with the AB5 type compound. Further, with respect to the system wherein the A-site is constituted by a mixture comprising a rare earth element and Mg, there are known a couple of publications as explained below.
Namely, J. Less-Common Metals, 73, (1980) 339 discloses a hydrogen-absorbing alloy having a composition represented by La1-xMgxNi2. However, this hydrogen-absorbing alloy is accompanied with a problem that due to its high stability in relative to hydrogen, hydrogen can be hardly released therefrom, thus making it difficult to fully desorb hydrogen at the occasion of discharging the secondary battery. On the other hand, there is also a report on a hydrogen-absorbing alloy having a composition of LaMg2Ni9 (a summary of lecture in the 120th Spring Meeting of Japan Institute of Metals, p.289 (1997). However, this hydrogen-absorbing alloy is accompanied with a problem that the degree of hydrogen absorption is relatively low.
Japanese Patent Unexamined Publication S/62-271348 discloses a hydrogen absorption electrode comprising a hydrogen-absorbing alloy represented by a general formula Mm1-xAxNiaCobMc, while Japanese Patent Unexamined Publication S/62-271349 discloses a hydrogen absorption electrode comprising a hydrogen-absorbing alloy represented by a general formula La1-xAxNiaCobMc.
However, a metal oxide-hydrogen secondary battery provided with any one of these hydrogen absorption electrodes is accompanied with a problem that it is low in discharge capacity and short in charge/discharge cycle life.
Further, International Re-publication No. WO97/03213 and U.S. Pat. No. 5,840,166 disclose a hydrogen-absorbing electrode comprising a hydrogen-absorbing alloy having a specific antiphase boundary and a composition represented by the following general formula (i). This hydrogen-absorbing alloy is said as having a crystal structure consisting of LaNi5, i.e. CaCu5 type single-phase.
(R1-xLx)(Ni1-yLy)zxe2x80x83xe2x80x83(i)
wherein R is at least one element selected from La, Ce, Pr and Nd; L is at least one element selected from Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc, Mg and Ca; M is at least one element selected from Co, Al, Mn, Fe, Cu, Zr, Ti, Mo, Si, V, Cr, Nb, Hf, Ta, W, B and C; and x, y and z are respectively a number satisfying the conditions of: 0.05xe2x89xa6xxe2x89xa60.4, 0xe2x89xa6yxe2x89xa60.5, 0xe2x89xa6z less than 4.5.
This hydrogen-absorbing alloy is manufactured by allowing a melt of the alloy represented by the general formula (i) to drop on the surface of a roll having a surface roughness of 30 to 150 xcexcm in mean maximum height Rmax, whereby cooling and solidifying the melt under cooling conditions: 50 to 500xc2x0 C. in supercooling degree and 1,000 to 10,000xc2x0 C./sec. in cooling rate, thus obtaining flakes having a thickness of 0.1 to 2.0 mm, which is then heat-treated. This publication also mentions that if the aforementioned manufacturing conditions are not met, the resultant alloy may have two phases, i.e. a LaNi5 type phase and a Ce2Ni7 type phase, and hence it is impossible to obtain an alloy constituted by LaNi5 type single phase.
However, a secondary battery equipped with a negative electrode comprising a hydrogen-absorbing alloy having a CaCu5 type crystal structure, a specific antiphase boundary and a composition represented by the aforementioned general formula (i) is accompanied with problems that it is low in discharge capacity and short in charge/discharge cycle life.
Additionally, Japanese Patent Unexamined Publication H/11-29832 discloses a hydrogen-absorbing material represented by the following general formula (ii) and having a hexagonal system wherein a space group is P6 3/mmc, i.e. a Ce2Ni7 type crystal structure.
(R1-XAX)2(Ni7-Y-Z-xcex1-xcex2MnYNbZBxcex1Cxcex2)nxe2x80x83xe2x80x83(ii)
wherein R is a rare earth element or a misch metal (Mm); A is at least one element selected from Mg, Ti, Zr, Th, Hf, Si and Ca; B is at least one element selected from Al and Cu; C is at least one element selected from Ga, Ge, In, Sn, Sb, Tl, Pb and Bi; and X, Y, Z, xcex1, xcex2 and n are respectively a number satisfying the conditions of: 0 less than Xxe2x89xa60.3, 0.3xe2x89xa6Yxe2x89xa61.5, 0 less than Zxe2x89xa60.3, 0xe2x89xa6xcex1xe2x89xa61.0, 0xe2x89xa6xcex2xe2x89xa61.0, and 0.9xe2x89xa6nxe2x89xa61.1.
In this hydrogen-absorbing alloy having a composition represented by the above formula (ii), the atomic ratio of Mn/(R+A) is in the range of 0.135 to 0.825.
However, since this hydrogen-absorbing alloy is poor in the reversibility of absorption/desorption reaction, the degree of hydrogen absorption and desorption is relatively low. Accordingly, a secondary battery equipped with a negative electrode comprising this hydrogen-absorbing alloy is accompanied with problems that the reversibility of absorption/desorption reaction is poor and the discharge voltage is also low, so that the discharge capacity thereof would be reduced.
Accordingly, an object of the present invention is to provide a hydrogen-absorbing alloy, which is capable of overcoming the problem of prior art that the desorption of hydrogen is suppressed due to an excessively high stability in relative to hydrogen in a hydrogen-absorbing alloy having a composition wherein the A-site is included in a relatively large ratio as compared with the composition of the AB5 type hydrogen-absorbing alloy; also capable of overcoming the problem of prior art that the hydrogen-absorbing alloy is vulnerable to corrosion and oxidation by the effect of an alkaline electrolyte; and capable of exhibiting an improved hydrogen absorption/desorption property.
Another object of the present invention is to provide a secondary battery which is large in capacity and excellent in charge/discharge cycles.
A further object of this invention is to provide a hybrid car and an electromobile, which are excellent in traveling performance such as fuel consumption, etc.
Namely, according to the present invention, there is provided a hydrogen-absorbing alloy comprising, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu5 type crystal structure) and a second phase having a rhombohedral crystal system, the hydrogen-absorbing alloy having a composition represented by the following general formula (1):
R1-a-bMgaTbNiZ-X-Y-xcex1M1XM2YMnxcex1xe2x80x83xe2x80x83(1)
wherein R is at least one kind of element selected from rare earth elements (which include Y); T is at least one element selected from the group consisting of Ca, Ti, Zr and Hf; M1 is at least one element selectedfrom the group consisting of Co and Fe; M2 is at least one element selected from the group consisting of Al, Ga, Zn, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, Li, P and S; and the atomic ratios of a, b, X, Y, xcex1 and Z are respectively a number satisfying the conditions of: 0.15xe2x89xa6axe2x89xa60.37, 0xe2x89xa6bxe2x89xa60.3, 0xe2x89xa6Xxe2x89xa61.3, 0xe2x89xa6Yxe2x89xa60.5, 0xe2x89xa6xcex1xe2x89xa60.135, and 2.5xe2x89xa6Zxe2x89xa64.2.
According to the present invention, there is also provided a secondary battery which comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte;
wherein the hydrogen-absorbing alloy comprises, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu5 type crystal structure) and a second phase having a rhombohedral crystal system; and the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (1).
According to the present invention, there is also provided a hybrid car comprising an electric driving means, and a power source for the electric driving means;
wherein the power source comprises a secondary battery which comprises a positive electrode, a negative electrode containing a hydrogen-absorbing alloy, and an alkaline electrolyte; and
wherein the hydrogen-absorbing alloy comprises, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu5 type crystal structure) and a second phase having a rhombohedral crystal system; and the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (1).
According to the present invention, there is also provided an electromobile comprising a secondary battery as a driving power source;
wherein the secondary battery comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; and
wherein the hydrogen-absorbing alloy comprises, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu5 type crystal structure) and a second phase having a rhombohedral crystal system; and the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (1).
Further, according to the present invention, there is provided a hydrogen-absorbing alloy exhibiting less than 0.15 (including 0) in intensity ratio to be calculated according to the following formula (2) and having a composition represented by the following general formula (3):
I1/I2xe2x80x83xe2x80x83(2)
wherein I2 is an intensity of a peak exhibiting a highest intensity in an X-ray diffraction using CuKxcex1-ray; and I1 is an intensity of a peak exhibiting a highest intensity within 2xcex8 of 8 to 13xc2x0, xcex8 being Bragg angle, in the X-ray diffraction;
R1-a-bMgaTbNiZ-XM3Xxe2x80x83xe2x80x83(3)
wherein R is at least one kind of element selected from rare earth elements (which include Y); T is at least one element selected from the group consisting of Ca, Ti, Zr and Hf; M3 is at least one element selected from the group consisting of Co, Mn, Fe, Al, Ga, Zn, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, Li, P and S; and the atomic ratios of a, b, X and Z are respectively a number satisfying the conditions of: 0.1xe2x89xa6axe2x89xa60.6, 0xe2x89xa6bxe2x89xa60.3, 0xe2x89xa6Xxe2x89xa62, and 2.5xe2x89xa6Zxe2x89xa64.
According to the present invention, there is also provided a secondary battery which comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte;
wherein the hydrogen-absorbing alloy exhibits less than 0.15 (including 0) in intensity ratio to be calculated according to the aforementioned formula (2) and has a composition represented by the aforementioned general formula (3).
According to the present invention, there is also provided a hybrid car comprising an electric driving means, and a power source for the electric driving means;
wherein the power source comprises a secondary battery which comprises a positive electrode, a negative electrode containing a hydrogen-absorbing alloy, and an alkaline electrolyte; and
wherein the hydrogen-absorbing alloy exhibits less than 0.15 (including 0) in intensity ratio to be calculated according to the aforementioned formula (2) and has a composition represented by the aforementioned general formula (3).
According to the present invention, there is also provided an electromobile comprising a secondary battery as a driving power source;
wherein the secondary battery comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; and
wherein the hydrogen-absorbing alloy exhibits less than 0.15 (including 0) in intensity ratio to be calculated according to the aforementioned formula (2) and has a composition represented by the aforementioned general formula (3).
Furthermore, according to the present invention, there is provided a hydrogen-absorbing alloy having a composition represented by the following general formula (4):
R1-aMgaNiZ-X-YAlXCoYM4xcex1xe2x80x83xe2x80x83(4)
wherein R is at least one kind of element selected from rare earth elements (which include Y) with a proviso that the content of Ce in the R is less than 20% by weight (including 0% by weight); M4 is at least one element selected from the group consisting of Mn, Fe, Al, Ga, Zn, Sn, Cu, Si, B, Nb, W, Ti, Zr, In, Mo, V, Cr, P and S; and the atomic ratios of a, X, Y, Z and xcex1 are respectively a number satisfying the conditions of: 0.15xe2x89xa6axe2x89xa60.33, 0.06xe2x89xa6Xxe2x89xa60.15, 0xe2x89xa6Yxe2x89xa60.2, 3.15 less than Zxe2x89xa63.55, and 0xe2x89xa6xcex1 less than 0.135.
According to the present invention, there is also provided a secondary battery which comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte;
wherein the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (4).
According to the present invention, there is also provided a hybrid car comprising an electric driving means, and a power source for the electric driving means;
wherein the power source comprises a secondary battery which comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; and
wherein the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (4).
According to the present invention, there is also provided an electromobile comprising a secondary battery as a driving power source;
wherein the secondary battery comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; and
wherein the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (4).
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.